This invention relates to a method of operating a nuclear reactor, and more particularly to a method of operating a nuclear reactor which is in less danger of the failure of nuclear fuel elements.
Hereunder, a method of operating a boiling water reactor will be described as an example. In the prior art method of operating the nuclear reactor, no special stipulation is made as to the power rise before the linear heat generating rate of nuclear fuel elements arranged in the core of the reactor (hereinbelow, simply termed the "linear heat generating rate") reaches about 240 W/cm. Where the nuclear reactor is operated at a linear heat generating rate of about 240 W/cm or above, provisions as stated below are made from the standpoint of preventing the failure of the nuclear fuel elements. When the linear heat generating rate is raised to or above about 240 W/cm for the first time, the power is gradually raised in a raising proportion of below about 1.8 W/cm/hour by the control of the flow rate of a recycling system. When the reactor power has been held constant at the linear heat rate of or above about 240 W/cm for about 12 hours, it is said that preconditioning has been made. Below the linear heat generating rate having been once preconditioned, the power rise can be carried out in a raising proportion of below (about 15% of the total power)/minute with preference taken of the flow rate control. Where the preconditioning is not made, control rods cannot be pulled out at the linear heat generating rate of or above about 240 W/cm.
It has been thought that, when the power of the nuclear reactor is raised as stated above, no failure of the nuclear fuel elements will occur. As described later, however, we have confirmed that the nuclear fuel elements are in danger of failure even below 240 W/cm.